Originally, the typewriter was a wholly mechanical device comprising an alpha-numeric keyboard, mechanical linkages between the keys and individual slugs of type, an inked ribbon and a paper carriage. Striking a key caused the corresponding typeface to impact on the inked ribbon located on the paper thereby printing the symbol on the typeface. The paper carriage was then moved one space, the process was repeated and the next symbol was printed. At the end of the line the carriage was returned, the paper was advanced one line and the process repeated to print the next line.
A major advance in typewriter technology was the development of the type ball and the daisy wheel. These did away with the individual mechanical linkage of one key to one corresponding typeface. Instead, the stroke of a key caused proper electromechanical positioning of the type ball or the daisy wheel so that the correct symbol was imprinted. These developments also did away with the cumbersome paper carriage moving from side to side. What remained, was a paper carriage which functioned to advance the paper one line at a time and the ink ribbon interposed between the paper and type ball or daisy wheel. Printing of the symbols on the paper was still by means of impact of the typeface on the ribbon and paper.
The advent of miniaturized electronics, microprocessors and sophisticated computer and display technology brought significant improvements to the input side of the typewriter, which acquired some of the attributes of a word processor. In a typical electronic typewriter such as the Smith-Corona PWP-80, as many as sixteen lines could be entered (typed), viewed on a flat panel display and edited prior to printing on the paper.
However, the method of actually committing data to paper remained in many instances the same: impact of a typeface on an inked ribbon laid on a sheet of paper. What also remained basically the same was the impact noise, vibration, the need frequently to change typewriter ribbons, and wear and tear on the typefaces.
In another kind of electronic typewriter, the data was printed thermally on paper. This involved the use of a dot matrix-like thermal print head which burned the data directly onto special thermal paper, or the use of a special thermal transfer ribbon interposed between the thermal print head and ordinary paper. In either case, the quality of the print was low and the use of specialized supplies was undesirable.
It is the object of this invention to eliminate the undesirable aspects of the prior art electronic typewriters. Thus, it is an object of the present invention to eliminate the mechanical output side of electronic typewriters which use a type ball or daisy wheel thereby doing away with the impact noise, vibration, wear on typefaces and the need to change ribbons. It is also an object of the present invention to eliminate the thermal print head and thermal transfer ribbon in electronic typewriters which print thermally.
This is accomplished, in this invention, by incorporating an electrophotographic or xerographic print unit in the typewriter housing in place of the mechanical or thermal print units previously used.
Related prior art includes devices in which electrophotographic image processors, i.e., xerographic printers, are connected as secondary output devices to word processors or computers. One such device is described in U.S. Pat. No. 4,714,940, Inoue et al, in which a copier is used to simultaneously or selectively copy an image displayed on a display screen and an image on an original. There the primary output device of the word processor is the display screen and the copier can copy the display. However this device and other prior art devices which rely on xerographic printers or copiers bear no relationship to a typewriter in form or in function.
It is an object of this invention to provide a typewriter in which the printing is accomplished by electrophotographic means rather than by mechanical or thermal means.
It is an object of this invention to eliminate printing impact noise and vibration.
It is also an object of this invention to provide a typewriter which does not require typewriter ribbons thereby eliminating any requirement for periodic replacement of ribbon cartridges.